I didn't find a picture of it at TrekCore but I thought I remember a tiny insert shot in DS9:Trials & Tribbleations showing an animation of a sensor "ping" coming from that spot. It's either when Sisko and Dax are on the bridge using the ship's internal scanners or when O'Brien is talking about beaming someone during a phase in the Enterprise's shield/sensor cycle.

Yes--the Enterprise's old-style Duotronic sensor array would send out sensor pings: one radiating radially in 360 degrees from the main hull, followed by one emanating from the bow of the ship--allowing the Defiant crew to beam about the Enterprise during that narrow time period between scans. The radial "ripples" that are portrayed are actually below the warp engines, so it seems these radiate from the lower sensor dome.

Since it's just a two-dimensional schematic, it's a little hard to tell if the pings are meant to be emanating from the bow of the ship, or from the engineering hull beneath it. But I think that the dish on the front of the engineering hull has been generally accepted to be a "deflector" dish, not a "sensor" dish.